An on/off power factor control (PFC) circuit is often used in certain types of motor-driven devices, such as pool pumps and blowers. The PFC circuit is located between rectifiers receiving alternating current (AC) input and bus capacitors and inverters providing current to the motor. If the PFC circuit's input voltage is low, resulting in higher-than-normal current in the PFC circuit, the PFC circuit goes into a current limit mode.
Specifically, the pump's PFC circuit senses voltage of the bus capacitors, also referred to as the output voltage of the PFC circuit. The load on the PFC circuit dictates a threshold input voltage at which the PFC circuit goes into the current limit mode. If the PFC circuit receives low line input voltage below the threshold for a particular load (e.g., low line input voltage, high load), the PFC circuit operates in the current limit mode, limiting current to a predetermined point that is above a normal maximum operating point. The PFC and associated components may be designed with tolerances capable of handling this higher-than-normal current in the short term, but the PFC and associated components are not designed to run at this PFC current limit point for extended periods of time, due to stress on components and effects on reliability and life of the motor parts. Furthermore, there is no way of knowing if the input voltage into the PFC circuit is too low until the PFC circuit goes into the current limit mode and bus capacitor voltage falls.